1. Field of the Invention
The present invention generally relates to a semiconductor device. More particularly, the present invention relates to a semiconductor device with a protection circuit protecting an internal circuit from static electricity generated at an input terminal.
2. Description of the Background Art
A conventional TFT (thin film transistor) of an active matrix type liquid crystal panel has been made of amorphous silicon. Recently, however, formation of a TFT from polysilicon has been under consideration. Conventionally, a scan line drive circuit or a data line drive circuit or the like has been configured of an LSI made of crystalline silicon and provided separately from a liquid crystal panel made of amorphous silicon. Since a mobility of polysilicon is approximately 100 times higher than that of amorphous silicon, however, a liquid crystal panel, a scan line drive circuit, a data line drive circuit or the like can be made of polysilicon to obtain one LCD (liquid crystal display) module.
A polysilicon TFT, however, exhibits a wide variation in TFT characteristics such as a threshold voltage or a mobility. Thus, a wide variation in a current consumption of the LCD module results. Therefore, it is of the utmost importance to accurately inspect whether or not the current consumption of the LCD module satisfies the standard value.
In a conventional array inspection, after charging a capacitor provided corresponding to each liquid crystal cell, a discharge current is detected. Based on a result of the detection, an inspection is performed as to whether or not the array is normal. The inspection time, however, can significantly be reduced, if the current consumption of the LCD module is inspected prior to this array inspection so that the conventional array inspection can be omitted when the inspection of the current consumption detects an unsatisfactory value. In this sense as well, an accurate detection of the current consumption of the LCD module is important.
Furthermore, a gate oxide film of the polysilicon TFT is thinner than that of an amorphous silicon TFT. Accordingly, the gate oxide film of the polysilicon TFT is more susceptible to damage from static electricity. As a method of preventing damage to the TFT from static electricity in an array manufacturing process, a method of short-circuiting terminals has been provided.
As a method of applying a voltage to a terminal in an array inspection as well as preventing damage to a TFT from static electricity, the following have been provided, i.e., a method of connecting a resistance element between each terminal and a conductor pattern, and a method of connecting two diodes in opposite directions in parallel between each terminal and a conductor pattern (see, for example, Japanese Patent Laying-Open No. 11-119257).
In order to accurately measure the current consumption of the LCD module, a resistance value of a resistance element or a diode needs to be high. The high resistance value of the resistance element or the diode, however, makes it difficult to flow static electricity out. This results in the LCD module having a low resistance to static electricity.